Subject: Re: [RFC 1/4] Add usb_get_address and usb_set_address support

From: Oliver Neukum <[email-masked]>
Date: Wed, 21 Aug 2019 11:08:18 +0200

Am Dienstag, den 20.08.2019, 22:18 +0000 schrieb
[email-masked]:
> The core USB driver message.c is missing get/set address functionality

This should go into usbnet. The CDC parser is where it is because
it is needed for serial and network devices. As serial devices
do not have a MAC, this can go into usbnet.

> that stops ifconfig from being able to push MAC addresses out to USB
> based ethernet devices.  Without this functionality, some USB devices
> stop responding to ethernet packets when using ifconfig to change MAC
> addresses.  This has been tested with a Dell Universal Dock D6000.
> 
> Signed-off-by: Charles Hyde <[email-masked]>
> Cc: Mario Limonciello <[email-masked]>
> Cc: Greg Kroah-Hartman <[email-masked]>
> Cc: [email-masked]
> ---
>  drivers/usb/core/message.c | 59 ++++++++++++++++++++++++++++++++++++++
>  include/linux/usb.h        |  3 ++
>  2 files changed, 62 insertions(+)
> 
> diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
> index 5adf489428aa..eea775234b09 100644
> --- a/drivers/usb/core/message.c
> +++ b/drivers/usb/core/message.c
> @@ -1085,6 +1085,65 @@ int usb_clear_halt(struct usb_device *dev, int pipe)
>  }
>  EXPORT_SYMBOL_GPL(usb_clear_halt);
>  
> +/**
> + * usb_get_address - 
> + * @dev: device whose endpoint is halted

Which endpoint?

> + * @mac: buffer for containing 
> + * Context: !in_interrupt ()
> + *
> + * This will attempt to get the six byte MAC address from a USB device's
> + * ethernet controller using GET_NET_ADDRESS command.
> + *
> + * This call is synchronous, and may not be used in an interrupt context.
> + *
> + * Return: Zero on success, or else the status code returned by the

Well, I am afraid it will return 6 on success.

> + * underlying usb_control_msg() call.
> + */
> +int usb_get_address(struct usb_device *dev, unsigned char * mac)
> +{
> +	int ret = -ENOMEM;

Initialization is unnecessary here.

> +	unsigned char *tbuf = kmalloc(256, GFP_NOIO);

If you intentionally picked a safety margin of 42 times, this
is cool. Otherwise it is a litttle much.

> +
> +	if (!tbuf)
> +		return -ENOMEM;
> +
> +	ret = usb_control_msg(dev, usb_sndctrlpipe(dev, 0),
> +			USB_CDC_GET_NET_ADDRESS,
> +			USB_DIR_IN | USB_TYPE_CLASS | USB_RECIP_INTERFACE,
> +			0, USB_REQ_SET_ADDRESS, tbuf, 256,
> +			USB_CTRL_GET_TIMEOUT);
> +	if (ret == 6)
> +		memcpy(mac, tbuf, 6);

You cannot ignore the case of devices sending more or less than 6
bytes.

	Regards
		Oliver